San Luis Valley aquifer system primer

San Luis Valley via National Geographic

From the Rio Grande Basin Roundtable (Helen Smith) via The Valley Courier:

Water is the glue that holds the San Luis Valley together. It is vital to the people, the economy, lifestyle and even the physical landscape of the Valley itself.

There are two aquifers that lie beneath the Valley floor. One is the confined aquifer that is trapped below a series of clay lenses deep beneath the Valley floor. The other is the unconfined aquifer that is generally found within the first 100 feet of the surface. Without the water from these aquifers, the San Luis Valley would very likely not be the agricultural workhorse that we know today.

There are also unique geological structures such as Rio Grande Rift that contributes to when and where water travels throughout the Valley subsurface. Aquifers are key, particularly the unconfined. The water of the unconfined aquifer functions very much like surface water. The recharge of this important commodity comes from the mountains and the snow that brings down their runoff. The unconfined aquifer supplies 85 percent of agricultural well water. The largest concentration of these wells lies within Sub-district #1.

The confined aquifer lies beneath the unconfined aquifer. There are clay layers that separate the aquifers. Historic Alamosa Lake is likely responsible for the formation of these layers. The water that lies beneath the surface is heavily relied upon by the agricultural community. There are also differences in how each of the aquifers react. In addition, any well in the San Luis Valley inevitably impacts the river flow at some point.

As a Valley native from Saguache, Allen Davey of Davis Engineering Services has studied the San Luis Valley aquifer system extensively. He also has a great deal of background on the Valley’s water issues. Davey points out that the aquifers and well levels have been monitored since 1970, when accurate measurements were first available. Since that time, there have been notable trends in the increase and decrease of the aquifer and well levels. The water table itself has seen a significant and steady decline partly due to the sheer number of wells that have been drilled. More water has been taken than replaced. The worst decrease was the extreme drought that began in 2002. Historically speaking, demand has simply outweighed supply. Because of these factors, there are now big implications for the future.

Davey also explained that the aquifers are situated very much like a bowl of water. This means that there is pressure that pushes the water upward from beneath the clay and downward pressure from the surface. The result is wells in the confined aquifer have high amounts of pressure, the result of which is artesian flow. Both confined and unconfined wells are heavily relied upon especially for agriculture irrigation. This has resulted in a widening gap between the aquifer waters and the surface.

Because this gap between the water and the surface has increased, it is now not impossible that there is potential for the Valley floor to begin sinking if the aquifer is not replenished. Rebuilding the aquifer system has now become even more necessary than many once thought. It has now become imperative that this issue be addressed. It is also critical that the recharge process is working properly.

The effort to replace the depletions and rebuild the aquifer is another piece to this puzzle. This is where sub-districts, the Rio Grande Water Conservation District and the pending well rules and regulations for Division 3 come in. The pending regulations for Division 3 require well users to replace their depletions. There is also a slow gain in the northern portions of the aquifer system being seen though studies and reports that Davis Engineering Services provides to the Rio Grande Water Conservation District. Because the well owners of Sub-district #1 have been replacing their depletions, Davey believes that the aquifer is headed in the right direction because of monitoring and reduced pumping. Replacing depletions will only help agriculture as well as Colorado’s obligation to the Rio Grande Compact.

The well rules for Division 3 and the replacement efforts are still a work in progress. However, it would appear that these measures are producing some results. The trial to finalize the rules for Division 3 is set for January of 2018. If and when these rules are approved, a great deal of change will arrive. Arguably, it is necessary change.

The future remains to be seen. There is certainly a great deal of importance in this matter when considering the agriculture, the people and the future of the San Luis Valley. This is a unique situation that will require a unique solution.

Helen Smith is the Outreach Specialist for the Rio Grande Basin Roundtable.

The Rio Grande Basin Roundtable meets the second Tuesday of every month. Meetings are located at the San Luis Valley Water Conservancy District office at 623 4th St. Alamosa. For more information visit http://www.RGBRT.org.

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